1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method for use in a recording unit including a circular recording medium, in particular, to a measuring apparatus and a measuring method for measuring performance characteristics of a recording unit including a circular recording medium such as a hard disk, a floppy disk or an optical disk such as CD, DVD, a magneto-optical disk (of ROM, write once type, rewriting type), or the like, and components such as a head for recording a data signal on the above recording medium, and the like.
2. Description of the Prior Art
Upon testing either a fixed type magnetism fixture magnetic disk drive unit (referred to as a hard disk unit hereinafter) for driving a hard disk, the above hard disk, or a magnetic head, there is the practice of evaluating the performance characteristics of the above hard disk, the disk drive unit and the circuit therefor, and the testing process includes the following steps:
(a) inserting a spindle into a center hole of the hard disk and supporting the magnetic head so as to electromagnetically couple the magnetic head with the surface of the hard disk in a non-contact manner;
(b) executing either a data writing process or a data reading process on the hard disk by means of the magnetic head while rotating the spindle by means of a spindle motor; and
(c) evaluating the performance characteristics of the hard disk unit including the hard disk.
As performance evaluation items the following ones can be enumerated. The performance evaluation items include the following:
(a) track average signal amplitude (Track Averaged Amplitude: referred to as a TAA hereinafter);
(b) asymmetry of a signal amplitude;
(c) pulse width (PW);
(d) asymmetry of a pulse width;
(e) base line;
(i) non-linear type bit shift amount (Non-linear Transition bit Shift: NLTS);
(g) overwrite characteristic (OverWrite: OW);
(h) bit error rate (Bit Error Rate: BER);
(i) margin, and so on.
When evaluating the performance of a hard disk, it is required to set parameters for measurement, and the parameters include the following:
(a) position of a magnetic head (referred to as a head position hereinafter);
(b) head angle (skew);
(c) spindle rotation speed;
(d) signal frequency;
(e) write data pattern;
(f) write current amount;
(g) write compensation amount (concretely, an amount of compensation for compensating for the write change timing);
(h) MR (Magnetic Resistance) head bias current, and so on.
In this case, the signal frequency, the write data pattern, the write current amount, the write compensation amount, the head position and the MR head bias current are write parameters for the hard disk, while the head position, the head angle and the MR head bias current are read parameters for the hard disk.
A procedure in measuring the above evaluation items has a sequence of parameter setting, writing onto a disk, reading out and evaluating the characteristics of the read signal. Conventionally, it has been a common practice to obtain a parameter dependency of the measured values of the evaluation items by changing set values of the above-mentioned parameters in small steps and repetitively executing a similar measurement. According to the conventional technique, such a measurement has been executed by writing data with one fixed parameter for one rotation of the disk when the spindle is rotated by one turn, and reading out the written data during another turn, thereby obtaining the measurement data for one point. By repeating this sequence a plurality of times while changing the parameter, a graph is obtained according to the measuring method based on the conventional technique (referred to as a first prior art hereinafter). That is, according to the conventional technique, one parameter has been set per one round of the track.
There is sometimes such a case that the state of a read element is disadvantageously changed by a magnetic field in the writing stage, then consequently this leads to an unstable characteristic (referred to as instability hereinafter). This phenomenon may be a kind that occurs only once per several times or another kind that occurs as a variation measurement. Therefore, in measuring such a characteristic it is a common practice to repeat the write and read operations many times, and then statistically evaluate the measured values of read signals. When measuring the above-mentioned instability by a conventional technique (referred to as a second prior art hereinafter), static data including the average value and variance of the measured value data are obtained by executing a plurality of times, a process including the steps of, first of all, writing desired data on the whole track of the disk, writing data which will be abandoned for a part of the track, and thereafter reading out the data on the rest of the track.
The above-mentioned prior art measuring method and measuring apparatus have had such a problem that the measuring time is relatively long.
Furthermore, when executing the measurement by switching the measurement item upon evaluating the performance characteristics of a hard disk, it takes much measuring time according to the prior art methods in an attempt at viewing the influences on the parameters requiring a significantly long time for convergence. As the parameters requiring a significantly long time for convergence, there can be enumerated the frequency, the head position and so on. For example, a relationship between the head position and the read signal amplitude is shown, where the relationship is called the track profile. Such a measurement (referred to as a third prior art hereinafter) takes a long time for moving the head position as compared with that of the rotation of the spindle, and this leads to such a problem that the measuring time is elongated.
In order to solve the above-described problems, the Japanese patent laid-open publication No. 11-053701 discloses, for example, a measuring apparatus for use in a recording unit for measuring performance characteristics of the recording unit including a record medium on which one track is divided into a plurality of sectors, where the measuring apparatus can measure performance characteristics at a speed higher than that of the prior art, by writing a write signal with a write parameter value changed for respective sectors, by reading out the written write signal, with predetermined read parameters for respective sectors, and by measuring the read-out write signal as a read signal.
Recently, a magnetic head in which a micro actuator (MA) is mounted as a new technology for higher concentration of the recording density of a hard disk has come into practical use. A magnetic head is mounted at the tip of a suspension, where the magnetic head is constituted by a slider 4c, a write element 4a and a read element (MR element) 4b, as shown in FIG. 21. A conventional system where these elements are moved together with the suspension for following the track cannot be no longer untreatable in the system having narrower tracks. Therefore, as shown in FIGS. 16 and 17, such an idea has been proposed that a small actuator which is called a micro actuator (MA) 6 is mounted at the tip of the suspension (or it may be provided at the root of the suspension) so as to facilitate following of the track by moving only the magnetic head 4.
It has become necessary for manufactures of the magnetic head 4 to measure the performance of the micro actuator 6 in addition to the characteristics of the conventional magnetic head 4 itself. As a typical measurement item, there is a static operational characteristic, and in order to obtain the characteristic, a relationship between a movement distance and a control voltage is measured by applying a control voltage Vc to the micro actuator 6 to determine the amount of distance by which the magnetic head 4 has moved, as shown in FIG. 18. A method for measuring the movement distance X of the micro actuator 6 according to a prior art therefor will be described in detail hereinafter.
First of all, the magnetic head 4 and a suspension 8 (referred to, as a whole, as a head gimbal assembly (HGA)) attached to an attachment jig 9b as shown in FIG. 19. The attachment jig 9b is attached to the top of a piezo-electric stage 9a, and the piezo-electric stage 9a has an ability for moving in a direction the same as that of the micro actuator 6. In addition, the movement distance of the piezo-electric stage 9a is calibrated, and therefore, can be precisely obtained. Then, as shown in FIG. 20, the magnetic head 4 is placed on the hard disk 1, and signal data is written in the track 202. Writing the same signal data is executed by the write element 4a of the magnetic head 4 (See FIG. 21).
As shown in FIGS. 23A to 23H, the magnetic head 4 is moved by movement of the piezo-electric stage 9a after signal data for one round of the track is written thereon. In order to perform this operation, it usually takes time required for several rounds of the hard disk 1, however, it is set to one round of the hard disk 1 in the example of FIGS. 23A to 23H. After the magnetic head 4 has moved to a desired location, the read element carries out reading out of data in the third round. In this case, usually, only the output amplitude TAA is measured. The average value of the output amplitude for one round of the track is called TAA as described above, and the TAA which is obtained in the third round is referred to as TAA (1). At the next round, the magnetic head 4 is moved to the next location by movement of the piezo-electric stage 9a, and the TAA is measured for the next round, which is referred to as TAA (2). In the same manner, TAA data at N points are measured, and then, a graph showing positions of the piezo-electric stage 9a on the horizontal axis and the TAA on the vertical axis is referred to as a track profile characteristic (FIG. 24). The following measurement is performed using this track profile characteristic as a reference.
From the track profile characteristic, a relative position of the read element 4b to the write element 4a can be seen. This relative position is designated by a dotted line of FIG. 24, and usually, has a finite value, which is called a read/write offset, since the read element 4b is not necessarily located at the same position as that of the write element 4a. In the above-mentioned operation, measurement is carried out at the reference position without application of any control voltage Vc to the micro actuator 6, namely, Vc=0V is applied thereto.
Next, as shown in FIGS. 25A to 25D, a predetermined control voltage Vc (1) is applied to the micro actuator 6, and in response to this, the micro actuator 6 moves. In this state, the track data is written. The written track 202 is located at a position shifted by the movement distance of the micro actuator 6 from the reference position. After that, the control voltage Vc which is applied to the micro actuator 6 is returned to 0V, so that the position of the micro actuator 6 is returned to the reference position. In the same manner as above, the track profile characteristic is measured while moving the piezo-electric stage 9a. The track profile characteristic TPF (1) obtained herein is shifted, as shown in FIG. 26, as compared with the above-measured track profile characteristic TPF (2). This shift is due to the movement of the micro actuator 6 by the applied control voltage Vc upon writing of the track 202, and therefore, by comparing the shift with the reference track profile characteristic TPF (2), the amount of movement of the micro actuator 6 can be found at the time of writing. The shift of the center of this characteristic (namely, the shift xe2x80x9cC2-C1xe2x80x9d from the position (center) of the read/write offset) is measured as X (1).
In the same manner, by measuring the movement distances X (1), X (2), X (3), . . . , X (M) of the total number of M points of the control voltage Vc while changing the control voltage Vc applied to the micro actuator 6 such as Vc (2), Vc (3), . . . , V (M), a desired characteristic of the movement distance relative to the control voltage can be obtained, as shown in FIG. 27.
The measuring method of the static characteristic of the micro actuator 6 according to the prior art is mentioned above, however, a method for obtaining the same characteristic may be considered by fixing the write element 4a at a predetermined reference position, by moving the micro actuator 6 with application of the control voltage Vc upon reading out of the track data, and by measuring the characteristic of the movement distance relative to the control voltage in the same manner using the piezo-electric stage 9a. 
According to the measuring method of the track profile of the prior art, the time for one round of the hard disk is required in order to measure the TAA of one point. For example, when the hard disk is rotated at a speed of 6000 rpm, a time of 10 ms is required. In order to obtain the value of the movement distance X (i) with a sufficient precision of the characteristic of the movement distance relative the control voltage, the minimum N=20 is required. In addition, the number of points of control voltages Vc for which the movement distances X of the micro actuator 6 are measured is not clearly defined, however, the measurements for ten control voltages Vc, for example, are considered to be necessary in order to measure the characteristic of the movement distance to voltage in a schematic graph form. In this case, the time for 20xc3x972xc3x9710 rounds is required at a minimum. When the rotation speed of the hard disk is set to 6000 rpm, the time required becomes 4 seconds. This is a long time which cannot be permitted for the throughput in competitive manufacturing line where several tenths of a second become critical. In other words, there is such a problem that an extremely large time is required for measuring the characteristic of the movement distance X of the micro actuator 6 relative to the control voltage Vc of the micro actuator 6 (hereinafter referred to as a characteristic of the movement distance to voltage).
An essential object of the present invention is therefore to provide a measuring apparatus and a measuring method for use in a recording unit, capable of shortening the time of measurement as compared with that of the prior art, upon measuring the characteristics of the control voltage to the movement distance of the recording unit.
In order to achieve the aforementioned objective, according to one aspect of the present invention, a measuring apparatus for measuring performance characteristics of a recording unit including a circular recording medium on which one track is divided into a plurality of sectors, the recording unit recording a data signal on the recording medium by using a magnetic head, the measuring apparatus comprising:
mechanism means for moving the magnetic head in a direction substantially perpendicular to a circumferential direction of the recording medium in response to a control signal;
writing means for writing a write signal for respective sectors while moving the magnetic head by outputting the control signal having different levels corresponding to respective sectors to the mechanism means; and
reading means for reading out the write signal written by the writing means, and for measuring a read-out write signal as a read signal relative to a position of the magnetic head.
In the above-mentioned apparatus, the reading means preferably measures characteristics of the read signal relative to the position of the magnetic head for respective sectors, by reading out the write signal written by the writing means for respective sectors while moving the magnetic head by changing the level of the control signal each time of one-round rotation of the recording medium, and by measuring the read-out write signal as a read signal relative to the position of the magnetic head.
The above-mentioned apparatus preferably further comprises calculating means for calculating the position of the magnetic head corresponding to a maximum value of the read signal for respective sectors based on the measured characteristics of the read signal relative to the position of the magnetic head for respective sectors, and for measuring characteristics of the position of the magnetic head relative to the level of the control signal based on a calculated position of the magnetic head for respective sectors.
In the above-mentioned apparatus, the writing means preferably generates a plurality of Sector trigger signals corresponding to the plurality of sectors by multiplying a frequency of an Index signal generated each time of one-round rotation of the recording medium, and for writing write signals for respective sectors based on the plurality of Sector trigger signals.
In the above-mentioned apparatus, the writing means preferably generates respective timing signals delayed respectively by a plurality of predetermined delay times from an Index signal generated each time of one-round rotation of the recording medium, and for writing write signals for respective sectors based on the respective timing signals.
In the above-mentioned apparatus, the mechanism means preferably comprises a micro actuator and a piezo-electric stage.
According to another aspect of the present invention, there is provided a measuring method for measuring performance characteristics of a recording unit including a circular recording medium on which one track is divided into a plurality of sectors, the recording unit recording a data signal on the recording medium by using a magnetic head, the measuring method including the steps of:
moving the magnetic head in a direction substantially perpendicular to a circumferential direction of the recording medium in response to a control signal by using mechanism means;
writing a write signal for respective sectors while moving the magnetic head by outputting the control signal having different levels corresponding to respective sectors; and
reading out the written write signal, and for measuring a read-out write signal as a read signal relative to a position of the magnetic head.
In the above-mentioned method, the reading step preferably includes a step of measuring characteristics of the read signal relative to the position of the magnetic head for respective sectors, by reading out the written write signal for respective sectors while moving the magnetic head by changing the level of the control signal each time of one-round rotation of the recording medium, and by measuring the read-out write signal as a read signal relative to the position of the magnetic head.
The above-mentioned method preferably further includes a step of calculating the position of the magnetic head corresponding to a maximum value of the read signal for respective sectors based on the measured characteristics of the read signal relative to the position of the magnetic head for respective sectors, and for measuring characteristics of the position of the magnetic head relative to the level of the control signal based on a calculated position of the magnetic head for respective sectors.
In the above-mentioned method, the writing step preferably includes a step of generating a plurality of Sector trigger signals corresponding to the plurality of sectors by multiplying a frequency of an Index signal generated each time of one-round rotation of the recording medium, and writing write signals for respective sectors based on the plurality of Sector trigger signals.
In the above-mentioned method, the writing step preferably includes a step of generating respective timing signals delayed respectively by a plurality of predetermined delay times from an Index signal generated each time of one-round rotation of the recording medium, and writing write signals for respective sectors based on the respective timing signals.
In the above-mentioned method, the mechanism means preferably comprises a micro actuator and a piezo-electric stage.